Key Idea: Topic 2.2 explains how ecosystems are organised, and why some ecosystems can recover (resilience) while others cross tipping points and collapse.
✅ Core definitions (exam must-know)
If a question mentions abiotic factors, it is about an ecosystem, not just a community.
🌍 Ecosystems as systems & scale
🛡️ What increases resilience?
Memorise the chain: Disturbance → resilience → recovery.
🦸 Keystone species
⚠️ Low resilience & tipping points
High marks come from linking ideas: biodiversity ↓ → resilience ↓ → tipping point risk ↑.
Community vs ecosystem: A community includes only the living organisms in an area, while an ecosystem includes the community plus abiotic factors such as soil, water, and climate. Three factors that increase ecosystem resilience: • High biodiversity (more species = more alternative pathways) • Complex food webs (less dependence on one species) • Genetic diversity within populations (greater adaptability) Keystone species & trophic cascade: A keystone species has a disproportionately large effect on its ecosystem. Removing it can cause a trophic cascade, where changes at one trophic level affect multiple other levels.